114070-71-2Relevant articles and documents
Influence of ortho Methyl and Isopropyl Substituents on the Reactivity of N-t-Butyl P-Arylphosphonamidic Chlorides with Isopropylamine and t-Butylamine: Steric Acceleration of Metaphosphonimidate Formation by an Elimination-Addition Mechanism; Contrasting Behaviour of N,N-Dimethyl P-A...
Freeman, Sally,Harger, Martin J.
, p. 1399 - 1406 (1987)
The two types of phosphonamidic chloride ArP(O)(Cl)NMe2, (5) and ArP(O)(Cl)NHBut (7) have been prepared with Ar=Ph, o-MeC6H4, 2,4,6-Me3C6H2, and 2,4,6-Pri3C6H2.Both types give the expected phosphonic diamide substitution products with PriNH2 and ButNH2 in MeCN, but the two types display contrasting reactivity.With ButNH2 the NMe2 substrates (5) become progressively less reactive as the degree of steric crowding increases, and although the decrease is quite small (70-fold overall) it seems consistent with an associative N2(P)> mechanism.These substrates react >=100 times faster with PriNH2, than with ButNH2 and in PriNH2-ButNH2 competitive experiments they give almost exclusively (>=99percent) the product derived from the less hindered PriNH2.For the NHBut substrates (7) with ButNH2, there is little difference in reactivity between the Ph and o-MeC6H4 compounds, and between the 2,4,6-Me3C6H2 and 2,4,6-Pri3C6H2 compounds, but remarkably the more crowded pair of substrates is the more reactive, by a factor of ca. 100.Also, in competitive experiments these substrates display relatively little preference for reaction with PriNH2.Here a dissociative elimination-addition mechanism, with a metaphosphonimidate intermediate, is seen to be important.A possible explanation of the steric acceleration is advanced.The ability of (7; Ar=Ph) to undergo substitution by elimination-addition makes possible the phosphonylation of unreactive nucleophiles such as ButOH and Pri2NH under mild conditions.
